1. Field of the Invention
The invention relates to a method of expanding a hot flue-gas flow in a turbine through which the flue-gas flow passes. In the turbine at least one structural component is cooled by an associated cooling-gas flow, which flows through the structural component and is fed from the latter to the flue-gas flow. A fuel is added in a metered fashion to the flue-gas flow in the turbine for temperature compensating purposed. The invention also relates to a corresponding gas turbine system.
Such a method and such a turbine system are disclosed in Published, Non-Prosecuted German Patent Applications DE 43 30 612 A1 and DE 43 30 613 A1. There are references recited therein pertaining to the field of the invention, which are also of importance in connection to the invention described below. Reference is therefore specifically made to the entire contents of both publications.
The Published, Non-Prosecuted German Patent Application DE 43 30 613 A1 relates to so-called interheating, with the aim of increasing the exhaust-gas temperature of the flue-gas flow in order to make a subsequent steam process more efficient. The principle of reheating consists in increasing the temperature of the combustion air in the combustion chamber and additionally increasing the temperature again at a lower pressure during the expansion phase of the burned combustion air. This ultimately results in a higher outlet temperature of the flue-gas flow after complete expansion to atmospheric pressure. Such reheating is preferably effected up to the maximum temperature permissible in the gas turbine, as a result of which an especially high outlet temperature of the flue-gas flow is achieved.
A gas turbine having a plurality of compressors fluidically connected in series is disclosed in the published British Patent Application GB 2 288 640 A. In that turbine, multiple inter-heating takes place, with the aim of achieving an especially high outlet temperature of the flue-gas. As in the Published, Non-Prosecuted German Patent Application DE 43 30 613 A1, the aim of achieving an increase in the efficiency via a change in the thermodynamic process is thus described. In particular, the multiple reheating is intended to permit a modification of the Joule process and an approximation of the so-called Ericson process. The temperature of the flue-gas flow is preferably increased here to about 1400.degree. C. in each individual gas turbine. Incomplete combustion takes place in a combustion chamber disposed between the gas turbines and the compressors, where all of the fuel is fed to the combustion chamber. An air quantity fed via a respective compressor flow is in each case greater than the air quantity required for the cooling. The published British patent application No. 2 288 640 A therefore pursues the aim of compensating for a temperature loss as a result of the occurring expansion.
A gas turbine whose axial flow duct is divided into two sectional passages through which the moving blades move is described in German Patent DE 35 00 447 C2. The flue gas flows in a combustion-gas sector and cooling air for cooling the moving blades flows in an air sector. A reduced output of the turbine on account of the fact that the hot combustion air is not admitted to the moving blades over the entire cross-section of the flow passage but only in the combustion-gas sector is believed to be rectified by a modification of the gas turbine specified. To this end, combustion chambers disposed axially one behind the other are provided in the combustion-chamber sector. Therefore, the German Patent DE 35 00 447 C2, like the Published, Non-Prosecuted German Patent Application DE 43 30 613 A1, also deals with a form of interheating, which in this case, however, is restricted solely to the combustion-gas sector.